Method of manufacturing fluorescent screens of cathode ray tubes

ABSTRACT

A fluorescent screen of a cathode ray tube is prepared by forming a film of photosensitive sticky substance, for example, an aqueous solution of a copolymer of a complex salt of diazonium salt and zinc chloride, oN an inner surface of a face plate of the tube, exposing the film to light to render portions thereof sticky, applying a powdery substance, for example, .[.phosphors of three colors.]. .Iadd.graphite.Iaddend., onto the film to cause the powdery substance to adhere to the portions of the film rendered sticky, removing excess powder to form a film pattern of the powdery substance, causing the substance responsible for stickiness to ooze out onto the film pattern, applying another powdery substance, for example, .[.graphite.]. .Iadd.titanium oxide .Iaddend.onto the film pattern and removing an excess of another powder substance, thus forming the fluorescent screen. The invention is applicable to the manufacture of a fluorescent screen for use in a color picture tube, a monochromatic picture tube and a penetration tube.

.Iadd.This is a reissue of application Ser. No. 361,269 filed Mar. 24,1982, now U.S. Pat. No. 4,391,885. .Iaddend.

BACKGROUND OF THE INVENTION

This invention relates to a method of manufacturing a fluorescnt screen,particularly of a multilayer construction of a cathode ray tube.

Multilayer fluorescent screen has been used in various types of cathoderay tubes. For example, in a penetration tube, two or three phosphorlayers emitting light of different colors are laminated with nonluminouslayers interleaved. In many cathode ray tubes, an aluminum film, calleda metal back, is formed on the side of a fluorescent screen facing anelectron gun structure. In such a case, a filming layer acting as asubstrate is formed on the fluorescent screen.

To prepare such a multilayer construction, various techniques have beenused for different purposes. These techniques, however, requirecomplicated steps, thus requiring complicated installations, increasingmanufacturing cost and decreasing yielding rate.

.[.BACKGROUND.]. .Iadd.SUMMARY .Iaddend.OF THE INVENTION

It is, therefore, an object of this invention to provide a novel methodof manufacturing a fluorescent screen of a cathode ray tube capable ofreadily manufacturing a fluorescent screen of a multilayer construction.

According to this invention, there is provided a method of manufacturinga fluorescent screen of a cathode ray tube comprising the stepsof.Iadd.: .Iaddend.forming a film of photosensitive substance thatexhibits stickiness when exposed to light on an inner surface of a faceplate of the tube; exposing the film to light to render portions thereofsticky; applying a powdery substance onto the film to cause thesubstance to adhere to the portions of the film rendered sticky;removing excess powder to form a film pattern of the powdery substance;causing the substance responsible for stickiness to ooze out onto thefilm pattern; applying another powdery substance onto the film pattern;and removing excess of .Iadd.said .Iaddend.another powdery substance,thus forming the fluorescent screen.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1a to 1d illustrate a preparation process of a fluorescent screenaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An aqueous solution of a polymer of a complex salt of diazonium salt andzinc chloride is coated on a substrate 10 of glass or the like (FIG.1a). When the film 11 is dried and then partly irradiated with lightthrough an apertured mask 12, zinc chloride formed as a result ofphotodecomposition absorbs moisture so that portions 13 of the filmexposed to light becomes sticky (FIG. 1b). A dry powder is sprayed onthe film in this state and excess powder is removed by compressed air toform a desired pattern 14 of the powder on the film (FIG. 1c). When thefilm is left .[.standstill.]. .Iadd.stationary.Iaddend., the substanceresponsible for stickiness or sticky liquid rises along the surfaces ofthe particles that constitute the film owing to capillary phenomenon,and when the film is sufficiently thin, the sticky liquid would ooze outto the top surface of the film with the result that the film itselfmanifests stickiness. When another type of powder is applied to such asticky film and excess particles are blown away with air, a second film15 of another type of the powder is formed on the first film (FIG. 1d).When the second film is sufficiently thin the sticky liquid furtheroozes out to the surface of the second film so that still another powdercan be applied. The above preparation process can be repeated until thesticky liquid does not ooze out to prepare a multilayer film. Where aphotosensitive sticky substance is coated on the substrate to asufficient thickness and the amount of exposure light is increased, theamount of the sticky liquid increases so that it is possible to increasethe number of layers. Accordingly, the number of layers can bedetermined as desired by varying the thickness and concentration of thephotosensitive sticky substance and the amount of exposure light.

For better understanding of the invention, the following examples aregiven.

EXAMPLE 1

An aqueous solution of a photosensitive sticky substance having thefollowing composition was coated on the inner surface of the panel glassof the color picture tube and the thickness of the film was adjusted to0.5 to 0.8 microns with a conventional rotary spinning machine, followedby drying.

    ______________________________________                                        arginic acid-polypropylene glycol ester                                                              0.2     wt. %                                          polyvinyl alcohol      0.06    wt. %                                          P--dimethyl aminobenzene diazonium                                                                   3.3     wt. %                                          chloride, zinc chloride                                                       water                  balance                                                ______________________________________                                    

After mounting a stripe shadow mask, portions of the film .Iadd.otherthan the portion .Iaddend.approximately corresponding to locations forthree colors of green, blue and red .Iadd.stripes .Iaddend.weresuccessively exposed to light. At this time, the position of a light.[.force.]. .Iadd.source was shifted .Iaddend.from the ordinarypositions of the light source for exposure of portions at which stripesof phosphors of respective colors are to be formed, by half the distancebetween the positions in a direction perpendicular to the stripes. Afterexposure, the shadow mask was dismounted and a fine powder of graphitehaving a particle size of 0.2 to 0.3 microns was sprayed and excesspowder was removed by compressed air, thus forming an ordinary blackmatrix stripe. After one minute, sticky liquid created by the previousexposure oozed out onto the .Iadd.surface of the .Iaddend.black matrixstripe. Then, a fine powder of titanium oxide having a particle size of0.1 to 0.2 microns was applied and excess powder was removed bycompressed air to form titanium oxide layer acting as a reflection layeron the graphite layer. Thereafter, the film was exposed to light in aconventional manner to form phosphor stripes of three colors.Iadd.between black matrix stripes.Iaddend.. Conventional steps werefollowed to complete a fluorescent screen.

EXAMPLE 2

This example concerns manufacture of a penetration tube. Firstly, anaqueous solution of photosensitive sticky substance having the samecomposition as in Example 1 was applied to the inner surface of a faceplate of the tube to a thickness of 1 to 1.5 microns, the resulting filmwas dried and then uniformly exposed to light. A powder of phosphoracting as a blue phosphor and consisting of zinc sulfide and silver andhaving a particle size of about 0.1 micron was sprayed to a thickness ofabout 0.9 microns and excess powder was removed by compressed air. Theassembly was left standstill for about one minute to cause the stickyliquid to ooze out. Then, a powder of silica having a particle size ofabout 0.05 microns was applied to a thickness of about 0.25 microns andexcess powder was removed by compressed air to form silica films actingas barriers for increasing the potential difference between phosphorlayers. The assembly was left .[.standstill.]. .Iadd.stationary.Iaddend.for one minute to cause the sticky liquid to ooze out. Then, apowder of green phosphor consisting of zinc silicate and manganese wasapplied to a thickness of about 0.25 microns and then developed. Theassembly was left .[.standstill.]. .Iadd.stationary .Iaddend.for 30seconds, and then in the same manner as described above, a powder ofsilica was applied to a thickness of about 0.7 microns to form a silicafilm. Then, the assembly was left standstill for one minute, and apowder of red phosphor having a particle size of 0.1 micron andconsisting of silicates of magnesium, cadmium and zinc, and manganesewas applied to a thickness of about 0.5 microns to form a multilayerconstruction, followed by predetermined steps to obtain a fluorescentscreen.

EXAMPLE 3

An aqueous solution of the photosensitive sticky substance, the same asthat of Example 1, was coated to a thickness of about 0.5 to 0.6 micronson the inner surface of the face plate of a monochromatic cathode raytube and then dried. After uniformly exposing the resulting film tolight, a powder of white phosphor having a particle size of about 7 to 8microns and consisting of a mixture of zinc sulfide-silver, zincsulfide-copper, and aluminam was sprayed to a thickness of about 15 to20 microns, and excess powder was removed with compressed air. After theassembly was left .[.standstill.]. .Iadd.stationary .Iaddend.for twominutes, a fine powder of .[.isobuthyl.]. .Iadd.isobutyl.Iaddend.methacrylate resin having a particle size of about 0.05 micronswas applied to a thickness of about 5 microns and the resulting film wasthen developed. Thereafter, the face plate was heated to 85° C. to fusetogether the particles of the resin for forming a continuous film actingas a filming layer on the phosphor film, followed by predetermined stepsto obtain a fluorescent screen.

It should be understood that the foregoing examples show only fewexamples of the method of this invention for preparing a fluorescentscreen of a multilayer construction, and that various types offluorescent screens can be prepared by adjusting the quantity of thesticky liquid by varying the quantity of the applied photosensitivesticky substance and the quantity of exposure light, or by changing thecombination of the powdery substances. For example, the filming layerdescribed in Example 3 can also be applied following the steps describedin Examples 1 and 2.

As described above, according to the method of manufacturing afluorescent screen of a cathode ray tube of this invention, a film ofphotosensitive sticky substance is exposed to light to render it sticky,then powders of various substances are applied to the sticky film, andexcess powders are removed to develope. After the sticky liquid hasoozed out to the surface of the film, another powder is applied againand then developed. In this manner, a multilayer fluorescent screenhaving any desired number of layers and consisting of differentmaterials can readily be prepared until the sticky liquid does not oozeout any more.

What is claimed is:
 1. A method of manufacturing a fluorescent screen of a cathode ray tube comprising the steps of:forming a film of photosensitive .[.sticky.]. substance that exhibits stickiness when exposed to light on an inner surface of a face plate of said tube; exposing said film to light to render portions thereof sticky; applying a powdery substance onto said film to cause said powdery substance to adhere to said portions of the film rendered sticky; removing excess powder to form a film pattern of said powdery substance; causing the substance responsible for stickiness to ooze out onto said film pattern; applying another powdery substance onto said film pattern; and removing an excess of said another powdery substance, thus forming said fluorescent screen.
 2. The method according to claim 1 wherein said photosensitive .[.sticky.]. substance comprises a compolymer of a complex salt of diazonium salt and zinc chloride.
 3. The method according to claim 1 wherein said film of photosensitive .[.sticky.]. substance has a thickness of about 0.5 to 0.8 microns.
 4. The method according to claim 1 wherein said powdery substance comprises .[.powders.]. .Iadd.a powder .Iaddend.of phosphors of .Iadd.one of .Iaddend.three colors of green, blue and red.
 5. The method according to claim .[.1.]. .Iadd.4 .Iaddend.wherein said another powdery substance comprises a powder of .[.graphite.]. .Iadd.silica.Iaddend..
 6. The method according to claim 5 which further comprises the step of applying a powder of .[.white substance onto a film of graphite to form a reflection layer.]. .Iadd.a phosphor of a second of said three colors.Iaddend..
 7. The method according to claim .[.1.]. .Iadd.6 .Iaddend.wherein .[.said.]. .Iadd.a second .Iaddend.another powdery substance .[.comprises.]. .Iadd.comprising .Iaddend.a powder of silica .Iadd.is applied to said phosphor of said second color.Iaddend.. .Iadd.
 8. A method according to claim 1 wherein said powdery substance comprises a powder of graphite and said another powdery substance comprises a powder of titanium oxide. .Iaddend. .Iadd.
 9. The method according to claim 1 wherein said powdery substance is a powder of a phosphor and said another powdery substance comprises an isobutyl methacrylate resin. .Iaddend. 